This invention generally relates to medical devices, and particularly to balloon catheters.
In percutaneous transluminal coronary angioplasty (PTCA) procedures, a guiding catheter is advanced until the distal tip of the guiding catheter is seated in the ostium of a desired coronary artery. A guidewire, positioned within an inner lumen of an dilatation catheter, is first advanced out of the distal end of the guiding catheter into the patient""s coronary artery until the distal end of the guidewire crosses a lesion to be dilated. Then the dilatation catheter having an inflatable balloon on the distal portion thereof is advanced into the patient""s coronary anatomy, over the previously introduced guidewire, until the balloon of the dilatation catheter is properly positioned across the lesion. Once properly positioned, the dilatation balloon is inflated with liquid one or more times to a predetermined size at relatively high pressures (e.g. greater than 8 atmospheres) so that the stenosis is compressed against the arterial wall and the wall expanded to open up the passageway. Generally, the inflated diameter of the balloon is approximately the same diameter as the native diameter of the body lumen being dilated so as to complete the dilatation but not overexpand the artery wall. Substantial, uncontrolled expansion of the balloon against the vessel wall can cause trauma to the vessel wall. After the balloon is finally deflated, blood flow resumes through the dilated artery and the dilatation catheter can be removed therefrom.
In such angioplasty procedures, there may be restenosis of the artery, i.e. reformation of the arterial blockage, which necessitates either another angioplasty procedure, or some other method of repairing or strengthening the dilated area. To reduce the restenosis rate and to strengthen the dilated area, physicians frequently implant an intravascular prosthesis, generally called a stent, inside the artery at the site of the lesion. Stents may also be used to repair vessels having an intimal flap or dissection or to generally strengthen a weakened section of a vessel. Stents are usually delivered to a desired location within a coronary artery in a contracted condition on a balloon of a catheter which is similar in many respects to a balloon angioplasty catheter, and expanded to a larger diameter by expansion of the balloon. The balloon is deflated to remove the catheter and the stent left in place within the artery at the site of the dilated lesion.
An important characteristic of balloon catheters or stent delivery catheters is the transmission of force from the proximal to the distal end of the catheter. This force transmission is generally referred to as catheter push, and significantly affects the physician""s ability to direct the catheter distal end into and across a stenosis in a blood vessel by manipulating the proximal end of the catheter outside the patient""s blood vessel. In the design of catheters, a tradeoff exists between the competing characteristics of shaft rigidity and flexibility. For example, catheter shafts must have sufficient rigidity to efficiently transmit force to enhance catheter push, in addition to sufficient flexibility to allow the catheter to bend and track within the tortuous body lumen. Catheter shafts which are disadvantageously rigid will resist bending and conforming to tortuous body lumens, which can inhibit catheter push and trackability and cause vessel injury. Consequently, catheter shaft rigidity and bendability must be balance to provide good push and prevent excessive bending resistance. It would be a significant advance to provide a catheter having improved pushability and trackability.
This invention is directed to a method of making a catheter having a catheter shaft, the method including axially (i.e., longitudinally) deflecting at least a section of the catheter shaft. The shaft section is axially deflected in a first radial direction on the shaft circumference one or more times. In a presently preferred embodiment, the method further includes axially deflecting the shaft section in at least a second radial direction on the shaft one or more times. The axial deflection produces stress in at least a section of the polymeric tubular member which reduces the push force of the shaft and catheter. The invention is also directed to a catheter shaft formed using the method of the invention, the catheter shaft generally comprising a polymeric tubular member. The polymeric tubular member has a section with deflection-induced stress from axial deflection of the section, so that the shaft has a push force reduced by the axial deflection-induced stress. In one embodiment, the section of the shaft having axial deflection-induced stress is adjacent to proximal and distal shaft sections which do not have the axial deflection-induced stress. The method of the invention produces a catheter having improved catheter push and trackability due to the reduced push force of the catheter shaft, which reduces bending resistance of the catheter without adversely reducing the pushability of the catheter. While discussed primarily in terms of a catheter shaft, the invention should be understood to include other catheter components which may be bonded to the catheter shaft, such as a balloon shaft and a soft distal tip.
In one embodiment of the invention, a desired section of the catheter shaft is axially deflected in a manner to produce stress only in the targeted section. Thus, a specific section such as a junction between catheter shaft sections or catheter components is axially deflected according to the method of the invention, to thereby lower the bending resistance at the junction, and preferably without affecting the adjacent sections of the catheter. In one embodiment, the junction has a higher bending resistance than adjacent sections of the catheter shaft before being axially deflected according to the method of the invention. Similarly, a section on the catheter that will be positioned at a specific location within the patient""s body lumen during use, such as the aortic arch of the aorta, can be can be axially deflected according to the method of the invention to lower the bending resistance at the section on the catheter shaft, preferably without affecting the adjacent sections of the catheter.
The stress, which in accordance with the invention is induced by axial deflection of the catheter shaft, is reflected in molecular orientation and/or plastic deformation in the catheter shaft. The shaft molecular orientation and/or plastic deformation gives directionality to the material properties of the shaft. For example, the axial deflection according to the method of the invention stretches or strains the shaft in an axial direction, such that the tensile properties of the shaft in a longitudinal direction perpendicular to the direction of the applied force are modified. Specifically, the molecular orientation and/or plastic deformation affects the axial tensile strength and the longitudinal tensile strength of the shaft by stressing the walls of the shaft, and affects the torsional rigidity of the shaft by stressing the material forming the shaft beyond the elastic limit of the material. The stress modifies the material dimensions and elasticity, and will lower tensile and torsional properties, and the modulus of the polymeric shaft. In a presently preferred embodiment, the stress induced molecular orientation and/or plastic deformation produced in the catheter shaft is in a direction aligned with the longitudinal axis of the shaft.
In one embodiment of the invention, the catheter shaft is axially deflected according to the method of the invention after assembly of the various catheter components. Thus, various targeted sections of the catheter, such as a junction between shaft sections, a junction between a shaft section and a distal tip, and a junction between a balloon shaft and the catheter shaft, may be modified according to the method of the invention by axially deflecting the section. Axially deflecting a section of the catheter after assembly of the catheter components according to the method of the invention facilitates determination of the specific location on the catheter shaft where the axial deflection-induced stress is desired. In contrast, if done before catheter assembly, catheter component tolerances and catheter assembly must be carefully controlled in order to assure that the axially deflected section is at the desired longitudinal location on the catheter. Moreover, processes performed during assembly of the catheter, such as fusion bonding of catheter components, may result in a relaxation of the residue of stress, and a loss of the state of molecular orientation and/or plastic deformation, produced by the axial deflection of the catheter components.